When a pipeline is rigidly connected to a floating vessel laying or recovering it in deep water, high bending moments occur at the connection. Due to the motion of the vessel these bending moments will oscillate and this introduces high degrees of stress and potential fatigue and failure of the pipeline.
The occurrence of these high bending moments and their resultant effects on the pipeline are particularly disadvantageous in connection with the recovery of pipelines for repair purposes. Currently the repair of pipelines involves the recovery of the pipeline and then using a hang-off clamp, which rigidly fixes (connects) the pipeline to the vessel. A repair can then be made to the pipeline “above” the hang-off clamp. This pipeline hang-off occurs generally through a moonpool at the side or over the stern of the vessel. The pipeline bending moments are concentrated in the area immediately below the hang-off clamp. The high bending moment in this area, with the resultant fatigue problems, causes a great limitation in the allowable operational seastate for such a hang-off and repair operation, or indeed any operation where such a hang-off is involved, for both pipelines and cables. This is particularly the case when a monohull vessel is used. For the conventional methods of hang-off and pipeline repair, a vessel spends a considerable amount of non-operational time “waiting for the weather”.
It is thus highly desirable to provide a means and method of reducing the bending moments of a pipeline or cable when rigidly hung off a vessel.